Repair Log: CPS1 No Sound

[DelsArcade]

Agreed that it seems to be a digital issue. Something is making the Z80 crash although it’s intermittent. Have you tried different sound EPROMs? Maybe one of them is flaky.

I doubt it's the sound roms, although I could re-burn to test. Reason being: When I swap to a 100% known working A board with this game, zero issues. If I swap this faulty A board onto another CPS1 (converted SFII to Ghouls and Ghosts) I can re-produce these intermittent sound issues. This is why I'm focusing on the A board as the culprit.

I did just get in 4 extension cables for the connectors so that I can get underneath to probe the A board while it's on. I couldn't before from underneath and some of the chips are surface mounted.

Any suggestions on what to probe first?

Del

 

[ShootTheCore]

You're in a tough spot for diagnosis where your sound cutout is intermittent - you'd have be probing the right spot exactly when the sound cuts out.

Just curious - when you tested the 100% working A board, did you leave it running for an hour? If you did and the sound didn't cut out then I agree that we can narrow our focus to just the A Board.

This diagram is pulled from the PCB Junkie website:
https://pcbjunkie.net/index.php/guides/capcom-cps-cps-1-repair-guide/


Rather than logic probing, I suggest getting some freeze spray and hitting each chip that's involved with sound in the lower middle of the A Board with the spray one at a time. If you're lucky, the blast of cold will cause the faulty chip to glitch and you'll know your culprit.

One more thing - make sure your board is getting a steady 5.0V . Some boards are more tolerant of low voltage than others.

 

[futasan]

Had the same issue on 2 mobos in the past, and solved it by replacing the sound oscillator.

 

[DelsArcade]

Had the same issue on 2 mobos in the past, and solved it by replacing the sound oscillator.

Curious where that's located on the PCB?

 

[futasan]

On top of the Oki

 

[ShootTheCore]

Curious where that's located on the PCB?

 

[DelsArcade]

Had the same issue on 2 mobos in the past, and solved it by replacing the sound oscillator.

Ah, the sound clock crystal. Gotcha. Don't think I have that on hand. I need to order a few.

Edit: Wondering if this is a suitable replacement or not: https://www.digikey.com/en/products/detail/ecs-inc/ECS-100AX-035/827253

Edit 2: Going to link this here too with a similar issue where the clock/oscillator part fixed it: https://www.aussiearcade.com/topic/75949-cps-1-audio-randomly-disappears-fixedsolved/

Del

 

[DelsArcade]

Whelp. I fixed it! It was indeed the sound oscillator/crystal. I used a known working one from a donor board.

Check out how rusted/corroded it was underneath:

I also got those extender cables in and work great:

Now I'm going to move on and start a thread on another CPS 1 PCB that has graphical glitches. I've also narrowed that one down to the A board. Go figure...

Thanks again for everyone's input!

Del

 

[ShootTheCore]

Great job!